1. Field of the Invention
The present invention relates to optical switches and, more particularly, to a method of constructing any arbitrary size scalable Mxc3x97N optical router/switch using modular components, and to a bi-directional optical component capable of being used in such a system.
2. Description of the Related Art
The past twenty years has witnessed an optical revolution in telecommunications. The widespread deployment of optical fibers in order to carry light signals over long distances has vastly increased the communication capabilities of present telecommunications systems. However, although the communication pathways have been changed to an optical core, rather than an electrical one, the elements used for routing or switching the optical signals have mostly remained electrical. In practice, this means the optical light signal must be converted to an electrical signal, and this electrical signal is routed and/or switched by an electrical router/switch; then the electrical signal is converted back into an optical signal for transmission over an optical fiber. These optical-to-electrical and electrical-to-optical conversion steps are wasteful of both time and resources.
To solve this problem, many companies have offered optical routers which perform routing/switching completely in the optical domain, without converting the communication signals from optical to electrical, and vice-versa. Many technologies have been developed to provide such optical routing/switching. The first commercially available optical routing technology was mechanically based and limited to 1xc3x972 and 2xc3x972 port sizes. These are based on beam expanding collimators and/or electromagnetically (e.g., stepper motor or solenoid) actuated mirrors, prisms, or collimators. Waveguide routing technologies are also becoming available now: silica-on-silicon waveguide or photonic lightwave circuit (PLC) technology (based on thermally induced changes in the refractive index of silica), lithium niobate technology (based on electrically induced changes in the refractive index). But these technologies suffer from limited scalability, high insertion loss, and high crosstalk. Liquid crystal optical switches (based on changing the polarization of incident light and then using polarization analyzers to route the polarized light) are also being developed, but they are complex and only low port count switches (1xc3x972 and 2xc3x972) are currently available. Other optical routing technologies being developed include III-V semiconductor-based waveguide switches, polymer-based thermo-optic digital waveguide switches, and semiconductor optical amplifier (SOA)-based gate switches.
Micro-electromechanical systems (MEMS) are rapidly establishing itself as the most attractive technology for optical switching since it allows low-loss large-port-count optical switching solutions at the lowest cost per port. Basically, a MEMS device is a mechanical integrated circuit where the actuation forces required to move the parts may be electrostatic, electromagnetic, or thermal. The basic technology is based on establishing semiconductor processes for manufacturing highly accurate miniaturized parts and uses material with excellent mechanical and electrical properties (Si, SiOx, and SiNx). Silicon-based MEMS devices can be produced with different process technologies, including bulk micromachining, in which mechanical structures are etched in single crystal silicon, and surface micromachining, in which epitaxial layers of polysilicon, silicon nitride, and silicon oxide are deposited, patterned, and selectively removed.
U.S. Pat. No. 6,259,835 to Jing (which is hereby incorporated by reference) describes a 1xc3x97N MEMS optical switch with one primary port, a plurality of secondary ports, and a plurality of optical reflectors. Any one of the optical reflectors, which may comprise mirrors or prisms, can be moved by an actuator into position to reflect an input light beam out through a corresponding secondary port, i.e. to direct or route the signal to a destination. For example, FIG. 1 shows a switch with Input Fiber 101 engaged in Input Port 105, and a plurality of mirrors (e.g., Mirror 110) placed adjacent to a plurality of output ports (e.g., Output Port 120) in which output fibers are engaged. Input light beam 150 (indicated by the dotted line) comes from Input Port 105, reflects off of Mirror 110, and exits through Output Port 120. Since each output port has a corresponding mirror and actuator, the input light beam can be routed to any of the N output ports. If none of the mirrors is put in the path of the beam, the beam will reflect off of the last mirror (which is set in place) and exit out of the last output port.
Bubble technology can be used to route light signals instead of mirrors or prisms in optical routers. For example, in U.S. Pat. No. 6,320,994 to Donald et al. (which is hereby incorporated by reference), at least three waveguides (an input waveguide, and two output waveguides) intersect at a gap having a predetermined width. The gap is either filled with a fluid (whereby input light will exit through one output) or a bubble (whereby input light will exit through the other output) formed by heating the fluid. U.S. Pat. No. 6,324,316 to Fouquet et al. (which is hereby incorporated by reference) shows a 4xc3x974 optical switch which uses bubble technology to route any of the four inputs to any of the four outputs. One shortcoming of Fouquet et al. is that, in most situations, if there are four input beams, at least one of these beams will cross at least one of the others after being reflected by a bubble. Although the interference caused by such interaction may be minimal, it is not non-existent (especially considering the beams are not orthogonal to each other), and such interference may become more problematic when technologies such as dense wavelength division multiplexing (DWDM) are used in combination with this switch.
Another problem with current optical routing technology is the lack of scalability, i.e., the inability for the technology to increase in size without becoming unduly complex. As examples, consider the two-dimensional MEMS cross-connect switch in FIG. 2A and the three-dimensional (3D) MEMS cross-connect switch in FIG. 2B. Both of these switches use mirrors. Mirror control for the 2D switch is binary and straightforward, but the trade-off for this simplicity is optical loss. Although the length of the light path only grows linearly with the number of input/output ports, the optical loss also grows rapidly due to the Gaussian nature of light. Because of this, 2D architectures are found to be impractical beyond 32 input and 32 output ports. Even though multiple stages of 32xc3x9732 2D switches could be put together to form a 1000-port 2D switch, the cumulative high optical losses make such an implementation impractical. By contrast, the 3D architecture of FIG. 2B greatly reduces the optical loss by making use of 3D space. In FIG. 2B, there are two banks of reflective mirrors which guide each light beam from any input port to any output port. Thus, there is a corresponding mirror for each of the input and output ports. Using this 3D architecture, switches with ports numbering in the thousands are possible. However, 3D architecture is complex, and becomes increasingly complex as the number of ports increases. Furthermore, such 3D optical switches are not modular in the sense that modular components can be added together to form larger routers. It makes more sense to simply built a larger 3D optical switch. But in such a large 3D optical switch, if only one mirror is out of alignment, or there is a problem with just a few mirrors, the entire switch must be taken out of service in order to fix it.
Even when conventional optical systems use modular components to construct an optical router, the resulting optical router is limited by other practical considerations. As an example, consider U.S. Pat. No. 5,771,320 to Stone (which is hereby incorporated by reference) which describes a modular system for building an optical routers. FIG. 3 shows two Stone modules 310 and 350 connected together to form an 8xc3x978 optical router. Each module is a MUX/DEMUX, meaning that it can operate as a stacked demultiplexer (one input routed to one of many outputs) or a stacked multiplexer (one of many inputs to one output). Module 310 in FIG. 3 is operating as a stacked DEMUX, where each level of the stack has one input, such as light beam 300 entering the top level of the stack, and eight outputs. Within each layer, a series of switchable diffractive grating stages 320A-C routes an input beam to one of the eight output ports. The grating stages 320A-C are separated by distances varying by powers of two; thus, the distance between the input port (which is also the first grating stage 320A) and the second grating stage 320B is twice the distance between the second grating stage 320B and the third grating stage 320C. The number of stages is n, where the number of outputs is 2xcfx80. FIG. 3 shows all the possible lightpaths of incoming light beam 300 on the top level of DEMUX module 310; however, in practice, only one route would be taken through the level (leading to only one out of the eight outputs).
The complete stacked first (DEMUX) module 310 has 8 input ports and 64 output ports and its 64 output ports are attached to the input ports of the second module 350, which is a MUX with 64 input ports and 8 output ports. The second module, MUX 350, is the same as the first module, DEMUX 310, except that the second module is turned around (so that the output becomes the input) and rotated 90 degrees (so that the stacked vertical layers become horizontal slices). The resulting combination allows any of the eight input beams to exit through any of the eight output ports without any blocking.
Stone""s optical router has limitations. First, because of the use of diffraction grating stages, the size of each layer increases exponentially as the number of outputs increase. Second, the number of inputs in each cubic module must be a power of 2 (i.e., 2xcfx80), and the number of outputs in each module must be 22n, limiting the possible sizes of modules. Third, to route one input beam, all n diffractive grating stages of each level must be activated. Fourth, Stone""s system is modular in only a limited sense, i.e., because each module can only be connected with modules of the same size and modules can not be put together to form larger modules (e.g., a 8xc3x9764 routing assembly can not be added to another 8xc3x9764 routing assembly to form a 16xc3x97128 routing assembly).
Therefore, there is a need for a system and method of building optical routers using modular components that are capable of constructing an optical router with any arbitrary number of input ports and output ports. Further, these modular components must be truly modular, i.e., they must be capable of interconnecting with other modules of any size. Further still, the modular components should be truly scalable, i.e., the size, complexity, and cost of the constructed optical router should not increase disproportionately as the number of I/O ports increase.
One object of the present invention is to provide a method of constructing an optical router with any arbitrary number of input ports and output ports from a plurality of optical components.
Another object of the present invention is to provide a modular optical router in which the router components can come in standard sizes, thereby reducing costs in the manufacturing of components and the building of modular optical routers.
Another object of the present invention is to provide a modular optical router construction method in which, if a portion of a modular optical router malfunctions or becomes defective, only the malfunctioning/defective optical component(s) will need to be replaced (instead of the entire router).
Yet another object of the present invention is to provide a modular optical router construction method which is truly scalable, i.e., the size, complexity, and cost of the constructed optical router should not increase disproportionately as the number of I/O ports increase.
These and other objects are achieved by the present invention which provides a modular optical router construction method in which the basic modules are a plurality of basic 1xc3x97N optical components which have input/output (I/O) ports which are capable of detachably interconnecting. In one aspect of the present invention, each of the basic 1xc3x97N optical components has a primary I/O port, N secondary I/O ports with a corresponding plurality of reflecting means, and a tertiary I/O port. Each reflecting means is either in an ON state or an OFF state. When in the ON state, the reflecting means either reflects a light beam to its corresponding secondary I/O port from the primary I/O port or reflects a light beam to the primary I/O port from its corresponding secondary I/O port. The tertiary I/O port is positioned so that any light beam input through the primary I/O port will be output through the tertiary I/O port if none of the reflecting means is in the ON state. The system and method may also use pass-through 1xc3x97N optical components, which are like the basic 1xc3x97N optical components but also include N quaternary I/O ports. Each quaternary I/O port has a corresponding secondary I/O port and is positioned such that any light beam input through the corresponding secondary I/O port will be output through the quaternary I/O port if none of the reflecting means is in the ON state.
In another aspect of the present invention, a bi-directional optical component capable of modular construction is provided. The bidirectional optical component has the same I/O ports as the basic 1xc3x97N optical component, but the bidirectional I/O ports are built to engage a duplex optical link (i.e., a link comprised of two optical fibers with signals going in two opposite directions). Furthermore, each secondary I/O port has a corresponding set of two reflecting means (one for each of the two directions of optical signal traffic).
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.